Scanning cylindrical antenna for a phase comparison guidance system

ABSTRACT

A circular or cylindrical scanning antenna array having circumferentially spaced radiating elements fed substantially in phase from a source of a carrier frequency with an imposed reference signal. In addition, an additional energy component is coupled in discretely to each radiating element through a fixed phase shifter for each such element. The fixed phase shifters have values beginning at zero for an arbitrary predetermined element location and then increasing in equal steps of theta where theta is the angular radiating element spacing about the perimeter. The additional energy fed through these phase shifters is modulated by a predetermined modulation signal to produce a single sideband. The result is a scanning, or rotating, amplitude modulated pattern similar to that used in the VOR or TACAN system.

United States Patent 1191 Howard Jan. 22, 1974 [75] Inventor: Shirly L. Howard, Rolling Hills Estates, Calif.

[73] Assignee: International Telephone and Telegraph Corporation, New York, NY.

22 Filed: Sept. 29, 1971 21 Appl. No.: 184,880

[52] US. Cl. 343/106 R, 343/100 SA Primary ExaminerBenjamin A. Borchelt Assistant ExaminerDenis H. McCabe Attorney, Agent, or FirmC. Cornell Remsen, Jr. et

[ 57] ABSTRACT A circular or cylindrical scanning antenna array having circumferentially spaced radiating elements fed substantially in phase from a source of a carrier frequency with an imposed reference signal. In addition. an additional energy component is coupled in discretely to each radiating element through a fixed phase shifter for each such element. The fixed phase shifters have values beginning at zero for an arbitrary predetermined element location and then increasing in equal steps of 6 where 0 is the angular radiating element spacing about the perimeter. The additional energy fed through these phase shifters is modulated by a predetermined modulation signal. to produce a single sideband. The result is a scanning, or rotating, amplitude modulated pattern similar to that used in the VCR or TACAN system.

6 Claims, 2 Drawing Figures PATENTEB JAN22 I974 SHEET 2 BF 2 SCANNING CYLINDRICAL ANTENNA FOR A PHASE COMPARISON GUIDANCE SYSTEM BACKGROUND OF THE INVENTION 1. Field of The Invention The invention relates to antenna systems, and'more particularly, to circular or cylindrical array systems producing a scanning or rotating predetermined pattern.

2. Description of The Prior Art In radar and other high frequency radio system applications, it is sometimes desired to radiate a symmetrical continuously rotating pattern having the appearance of amplitude modulated energy at a distant receiving station. Examples of such a system are the so-called VOR and TACAN systems for direction finding in air navigation.

US. Pat. No. 3,474,446 and US. Pat. application Ser. No. 36,050 filed May 11, 1970, now US. Pat. No. 3,670,336, relate to a type of electronic scanning for a cylindrical array antenna referred to. In the latter of these in particular, the theory of excitation of the elements of a cylindrical array to produce a predetermined desired audio frequency modulated carrier is given. In general, that type of excitation is germane to the type of antenna system used at air navigation ground stations, such as VOR or TACAN. In these systems, the modulation is applied to produce a rotating or apparently rotating shape pattern which is detectable as a straight-forward amplitude modulation component at a distant point such as in an aircraft receiving the signals. By making a phase comparison against a reference signal or reference mark, the aircraft is able to determine its bearing with respect to the VOR or TACAN ground station. TACAN differs from VOR in several respects, including the fact that it makes use of primary and a ninth harmonic modulation components for greater accuracy by providing a phase comparison vernier effect.

Generally speaking, the prior art antenna and scanning systems for effecting these results have been relatively complex and expensive.

SUMMARY It may be said to be the general objective of the present invention to produce a simplified and therefore less expensive antenna and scanning system of the general type adapted to VOR, TACAN, or general cylindrical array scanning ground station applications.

Basically, the present invention employs a circular or cylindrical array in which individual elements or columns of elements are arranged in juxtaposition about the perimeter of a circle or cylindrical surface. These elements are fed by a transmission line arrangement so that each receives a main unmodulated carrier and the reference signal in phase with all of the other radiators or columns of radiators. A small portion of the unmodulated carrier signal is tapped off by means ofa coupler and passed through a signal-controlled continuous phase shifter. The control signal for the said phase shifter is the modulation frequency for producing a single sideband required pattern rotation. The output of the controllable phase shifter is continuously phase advanced in accordance with this modulation signal, and that output is supplied by a second equal phase transmission line network to each of the said radiators (or columns of radiators acting as integral linear arrays) through a discrete fixed phase shifter discretely providing a phase shift proportional to the'angular position of each radiator from an aribtrary initial radiator position.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the block schematic diagram of FIG. 1, and assuming that the array is oriented essen tially for azimuth scanning or pattern rotation, the view of radiator and feed arrangements would be essentially a plan view in a horizontal plane.

For the sake of explanation without excessive duplication of hardware, the number of antenna elements or radiators distributed about the circular perimeter was arbitrarily shown as 16 in FIG. 1. In connection with the invention and system as described, it is to be understood that each of these antenna elements 1 through N can consist of a single radiating element such as a slot or a dipole, or the elements such as typically identified as l, 2 and 3, and N-l and N, could also consist of a linear array extending in the vertical plane, thereby producing a cylindrical array having certain predetermined beam characteristics in the elevation plane as well as the typical rotating patterncommonly identified with VOR or TACAN equipment in the azimuth plane. The use of linear arrays as the individual elements about the circular perimeter of the cylindrical array is shown in US. Pat. No. 3,474,446. The individual vertically oriented linear arrays in that event, are fed from a transmission line having a single input feedpoint. Thus, for the full cylindrical array arrangement in connection with FIG. 1, each individual antenna element may be thought of as drive point for a corresponding linear array of the type aforementioned.

A source of carrier m is introduced at terminal 4 and connects through a network of radio frequency transmission lines and power dividers to each antenna element. The said carrier energy passes through a first power division point D, which divides it equally between feedlines F and F Similarly F2 feeds F3 and F4 through another power division point, and F5 and F6 are fed from F3through still another power division point. Finally, F7 and F8 receive the power in F6 evenly as do F9 and F10 from F5. The lengths of these various segments of the transmission and power division network are designed such that the carrier energy arriving at antenna elements 1, 2 and 3, on up through N 1 and N is all in phase. A directional coupler 6 taps a small amount of the carrier power from 4 and feeds it to the variable phase shifter 10. This continuously controllable RF phase shifter (radio frequency phase shifter) may be either an analog or digital device. For the sake of explanation, it will be assumed to be an analog device, and the signal m is a continuous sinusoidal modulation frequency.

The suitable instrumentation for this continuous control phase shift device 10 would be provided by adaptation of the so-called Regia-Spencer phase shifter. That particular phase shifter is essentially an In-Waveguide device providing phase shift as a function of a D magnetic field through its ferrite core. The said DC field is established by the current through a solenoid coil surrounding the waveguide body along at least part of the length of the said ferrite core within. In the present invention, the modulation frequencies contemplated are in the low audio frequency range, and accordingly, the magnetic field variation can be readily achieved to produce the aforementioned function of this phase shift device.

Depending upon the percentage of modulation ultimately designed, the amplifier 20 may or may not be necessary. Generally speaking in the VCR or TACAN application, the amplifier 20 would probably be necessary because it is desired that the amount of carrier energy tapped off by the coupler 6 be relatively small and that the phase shift device 10 operate at a relatively low power level for economy and efficiency reasons. Then too, there is the fact that the driving point D2 is best supplied by a low impedance driver in view of the multiple power subdivisions taking place between D2 and the couplers Cl through CN adjacent to the individual antenna elements themselves.

Without going unnecessarily into details, it will be seen that a transmission and distribution line system F originating from point D2 essentially parallels the F network previously discussed, the same subscript numbers applying insofar as the power distribution among the various antenna elements is concerned. The point D2 also represents a pattern pointing or instantaneous position signal which can be provided to the navigation control equipment elsewhere and converted to a reference mark. Since the system is entirelypassive between the point D2 and the radiators themselves, the opportunity for phase drifts or other error to affect the correlation'accuracy of this reference signal is minimized.

The actual introduction of the modulated signal from the point D2 takes place at the couplers C1 through CN and the result is addition of the modulated carrier signal and the main carrier signal essentially at the individual antenna elements themselves. The result is that the phase of the variable phase shift device, or continuously controllable phase shift device 10, is advanced at the modulation rate co generating a single sideband equal to m m The coupling of this single sideband signal into the carrier frequency transmission line network immediately adjacent to the individual antenna elements produces a single sideband effect insofar as the radiated signal is concerned.

It will be noted that the phase of the coupled sideband is uniquely shifted by an amount varying from zero (or some nominal initial amount) to 360+ the said initial amount in incremental steps of onesixteenth of 360. Stated otherwise, individual fixed phase shift devices provide for phase shift of the said more antenna elements used about this perimeter and the progressive fixed phase shift would be correspondingly smaller between adjacent elements. The considerations in respect to the number of said antenna elements about the perimeter are set forth in the prior art patent literature referred to hereinbefore.

The system described in connection with FIG. 1 operates to create a unique phase angle as a function of azimuth, and as the said continuously controllable phase shift device shifts the entire group of sideband signals together, the result is to produce a scanning pattern in a phase relationship as noted at the distant receiving station which is related to the reference phase or marker of the system in accordance with the azimuth of the said receiving station in respect to the antenna array.

Referring now to FIG. 2, the introduction of a second modulation signal will be explained. In FIG. 2, the signal (0M on line 14 may be presumed to be the same signal as to in FIG. 1. If this signal is generated by a modulation frequency generator 11, a vernier tone may be generated synchronously in a harmonic modulation generator 13, synchronized to 1 1 by a signal on lead 12. In this way a harmonic signal m (such as a ninth harmonic typical of TACAN) is produced on lead 15. The function of w on line 14 into phase shifter 10 as applied to a fraction of the carrier energy extracted at 6 supplied to 10 through a lead 8, will be recognized as the equivalent to the showing of FIG. 1. If a similarly small or perhaps even smaller fraction of the carrier energy is extracted by an additional coupler 5, and is fed to another continuously controllable phase shift device 9 via lead 7, the signal on 16 will be an additional sidebandtype signal modulated from m via line 15. Thus the signal on line 16 could be identified as w m In FIG. 2, a portion of the feed system is duplicated from FIG. 1 in order to show its relationship with the additional structure.

An additional amplifier 18 operating on the signal at 16 (in the same way as amplifier 20 operates on the signal at 17) drives a third feed system from point D This third feed network branches similarly and the corresponding branches are marked with the same identifying symbol with double prime marks added, such as F F etc.

Typical fixed phase shifters S S and S are illustrated along with the corresponding couplers C C and C which inject the harmonic single sideband signal distributed by this third feed network into the corresponding antenna elements, in the same way as effected for the injection of the first modulation component. The phase shifters 8, through 8,, are constructed to introduce a multiple of the phase shift (measured in harmonic degrees) as compared to that introduced by C through C Thus adjacent radiating elements are spaced by 9 times as much fixed phase difference at m 35 at win- The coupling factors represented by couplers 5 and 6 and the reinjection couplers C through C and C through c,,,' will govern the percentage of modulation at the aperture of the entire array, and these factors may be selected or adjusted in accordance with design requirements.

Since the possibility exists for insertion phase'shift drift in the signal at 16 with respect to that at 17, additional structure may be added to correct for this phenomenon in any of several ways well known to those of skill in this art. One such way would involve the sampling of the signal 16 by a phase detector referenced by the signal on 17. Any error could be used to modify the signal on to ensure that the two modulation signals remain in phase synchronization. That modification could be introduced within 13 by a voltage controled phase shifter, for example.

VCR and TACAN systems compatible with this in vention include means for injecting F .M. reference data or North mark pulses; these subsystems operating from the 14 and 15 signals and announcing their reference data by separate carrier modulation schemes which are compatible but not a part of this invention.

It will be evident from this description that the present system in using only single sideband signals requires a modulation signal of only one-half the power required by normal double sideband systems. Moreover, radio frequency system bandwidth is also halved as compared to the normal double sideband system.

In accordance with standard antenna theory, the driving function of the system of FIG. 1 may be stated as follows:

V [1 A i i i m i o A amount of coupled modulation energy a, phase displacement of modulated energy at ith radiating element Modifications and variations of the present invention will suggest themselves to those skilled in this art. Accordingly, it is not intended that this description should be considered as limiting the scope of the present invention, the drawings and description being typical and illustrative only.

What is claimed is:

1. An omni-directional antenna array and scanning system for rotating a predetermined substantially symmetrical pattern in a first plane; comprising:

a plurality of antenna elements spaced around a substantially circular perimeter in said plane, said elements being arranged for radiation generally radially;

first feed means connected from a source of radio frequency carrier energy and connected to provide substantially equal power and phase energization of said elements;

controllable phase shift means connected through a coupler to receive a fraction of said carrier energy, said controllable phase shift means being responsive to a modulation frequency signal to produce a continuously phase shifted radio frequency signal as a function of said modulation frequency signal;

second feed means for substantially equal power distribution of said continuously phase shifted radio frequency signal to said antenna elements;

and a plurality of fixed phase shifters, one for each of said antenna elements, each of said fixed phase shifters connected discretely from said second feed means to a corresponding one of said antenna elements, the radio frequency phase shift of a first of said fixed shifters being an arbitrary value and each other of said fixed shifters providing an additional phase shift in degrees equal to 0, where 6 is the angle in degrees, of location of the corresponding antenna element measured with respect to said first fixed phase shifter through 360 about said perimeter.

2. Apparatus according to claim 1 in which said antenna elements are defined as being substantially equally angularly spaced about said perimeter.

3. Apparatus according to claim 2 in which said first plane is the azimuth plane and said antenna elements each comprise a linear array extending in a direction substantially normally to said first plane to form a cylindrical array.

4. Apparatus according to claim 3 including a dis crete directional coupler for connecting each of said fixed phase shifters to said corresponding antenna element, thereby to mix a predetermined phase modulated signal percentage into the energy radiated.

5. Apparatus according to claim 4 including an amplifier responsive to the output of said controllable phase shift means to permit said controllable phase shift means to operate at a relatively low power level and, at the same time, providing adequate drive power for said second feed means.

6. Apparatus according to claim 5 including means for generating a second modulation signal which is a synchronous harmonic of said modulation frequency signal, a second controllable phase shifter coupled to said source of carrier and connected to be controlled by said second modulation signal to produce a second continuously phase shifted radio frequency signal as a function of said harmonic frequency, third feed means for substantially equal power distribution of said sec ond continuously phase shifted radio frequency signal to said antenna elements, and a second plurality of fixed phase shifters having individual phase shifts at said harmonic frequency which are equal to the corresponding one of said fixed phase shifters multiplied by the order of said harmonic, said second fixed phase shifters being also discretely connected to corresponding ones of said antenna elements. 

1. An omni-directional antenna array and scanning system for rotating a predetermined substantially symmetrical pattern in a first plane; comprising: a plurality of antenna elements spaced around a substantially circular perimeter in said plane, said elements being arranged for radiation generally radially; first feed means connected from a source of radio frequency carrier energy and connected to provide substantially equal power and phase energization of said elements; controllable phase shift means connected through a coupler to receive a fraction of said carrier energy, said controllable phase shift means being responsive to a modulation frequency signal to produce a continuously phase shifted radio frequency signal as a function of said modulation frequency signal; second feed means for substantially equal power distribution of said continuously phase shifted radio frequency signal to said antenna elements; and a plurality of fixed phase shifters, one for each of said antenna elements, each of said fixed phase shifters connected discretely from said second feed means to a corresponding one of said antenna elements, the radio frequency phase shift of a first of said fixed shifters being an arbitrary value and each other of said fixed shifters providing an additional phase shift in degrees equal to theta , where theta is the angle in degrees, of location of the corresponding antenna element measured with respect to said first fixed phase shifter through 360* about said perimeter.
 2. Apparatus according to claim 1 in which said antenna elements are defined as being substantially equally angularly spaced about said perimeter.
 3. Apparatus according to claim 2 in which said first plane is the azimuth plane and said antenna elements each comprise a linear array extending in a direction substantially normally to said first plane to form a cylindrical array.
 4. Apparatus according to claim 3 including a discrete directional coupler for connecting each of said fixed phase shifters to said corresponding antenna element, thereby to mix a predetermined phase modulated signal percentage into the energy radiated.
 5. Apparatus according to claim 4 including an amplifier responsive to the output of said controllable phase shift means to permit said controllable phase shift means to operate at a relatively low power level and, at the same time, providing adequate drive power for said second feed means.
 6. Apparatus according to claim 5 including means for generating a second modulation signal which is a synchronous harmonic of said modulation frequency signal, a second controllable phase shifter coupled to said source of carrier and connected to be controlled by said second modulation signal to produce a second continuously phase shifted radio frequency signal as a function of said harmonic frequEncy, third feed means for substantially equal power distribution of said second continuously phase shifted radio frequency signal to said antenna elements, and a second plurality of fixed phase shifters having individual phase shifts at said harmonic frequency which are equal to the corresponding one of said fixed phase shifters multiplied by the order of said harmonic, said second fixed phase shifters being also discretely connected to corresponding ones of said antenna elements. 